Ethylene-higher .alpha.-olefin-polyene (EPDM) polymers are known for their excellent vulcanizate properties of oxygen and ozone resistance, weatherability, and heat and chemical resistance. Unfortunately, the polymers lack building tack, oil resistance, hot tear resistance, and high internal strength. These disadvantages prohibit the use of EPDM polymers in applications such as tires and automotive and industrial hosing, which have been dominated by high unsaturation diene rubbers such as natural rubber, styrene-butadiene rubbers, and polychloroprene. However, the diene rubbers have disadvantages in their lack of oxygen and ozone resistance and poor heat resistance and weatherability. A practical solution to the problems would be to physically blend the two types of polymers, cure the blend, and obtain a vulcanizate having the desirable properties of each type of polymer. One serious problem is cure incompatibility, or simply the inability of a cure system to sufficiently cure each type of polymer in the polymer blend, and to sufficiently co-vulcanize the types of polymers in the blend. Cure incompatibility is demonstrated by the failure of the vulcanizate to perform at a level predicted from a consideration of the ratios of the polymers in the blend. Often the performance will be much less than predicted, and even worse than the performance of either polymer alone. Poor co-vulcanization is readily apparent in the stress-strain (tensile, elongation) properties, flex-heat build up, and oil swell properties.
A major factor in cure incompatibility is the preference vulcanization accelerators show for one polymer over another, leading to over-cure of one polymer and undercure of the other polymer. To alleviate this preference, vulcanization accelerators having long chain hydrocarbon radicals (higher alkyl radicals) have been prepared and employed in polymer blends. U.S. Pat. No. 3,706,819 describes higher alkyl substituted thiuram disulfide and benzothiazyl sulfenamide accelerators, and U.S. Pat. No. 3,678,135 discloses higher alkyl dithiocarbamate accelerators. These accelerators, although they effectively co-cure the polymers in a blend, have other disadvantages in that they are either too scorchy for many uses or they provide too long of cure times. Higher alkyl thiocarbamylsulfenamides have been found to provide effective co-cure of the polymers in a blend, and also provide an improved balance between scorch safety and fast cure. This discovery is the subject of a related application for patent, Ser. No. 320,266 filed on Jan. 2, 1973. It has now been discovered that the positioning of the higher alkyl groups on the thiocarbamylsulfenamide compound significantly affects the compounds ability to co-vulcanize polymer blends of ethylene-higher .alpha.-olefin-polyene polymers and high unsaturation rubbers.